1. Field of the Invention
The present invention relates to a printing system, a printing apparatus, and a printing method.
2. Description of the Related Art
As a printing system that forms an image on both sides of a web, a web printing system that is disclosed in Japanese Patent No. 3680989 is suggested and is put to practical use. In the web printing system, two printing apparatuses are disposed in series, printing is performed on a first surface (front surface) of a web W using one printing apparatus (hereinafter, referred to as “first printing apparatus”) at a front stage, the web that is discharged from the first printing apparatus is then reversed by a reversing device T, the web W is fed to the other printing apparatus (hereinafter, referred to as “second printing apparatus”) at a rear stage, and printing is performed on a second surface (back surface) of the web using the second printing apparatus. This web printing system includes a control device that controls the operation of the first printing apparatus and the second printing apparatus.
Each of the printing apparatuses is an electrophotographic printing apparatus that heats, melts, and fixes a transferred toner image, and has a photosensitive drum, a developing device, and a heat fixing device. Specifically, each of the printing apparatuses has a photosensitive drum, a preheater, a heating roll, a pressurizing roll, and a puller roll. In this case, the preheater is a hot platen that preheats the web, and previously increases the temperature of the web and stabilizes fixing performance in the heating roll and the pressurizing roll.
In a web printing system 10, as an example of a printing preparation operation before printing starts, the photosensitive drum that is stopped at the time of non-printing rotates until the velocity thereof becomes a predetermined velocity, the temperature of the preheater of the heat fixing device is increased to a predetermined temperature, or the concentration of a toner in the developing device is adjusted to become a predetermined level at the time of printing.
In the web printing system that has the above configuration, if a printing operation is temporarily stopped due to occurrence of failure or an operator temporarily stops the printing operation due to other circumstances, the web is left loaded on the first printing apparatus and the second printing apparatus in a non-printing state. If this state is generated, the web that is stopped in the heat fixing device of the first printing apparatus is continuously heated by the preheater and the heating roll, the moisture of the web is evaporated as time passes, and a portion of the web is greatly thermally contracted and deformed.
In this state, if the printing restarts, the web having the portion (hereinafter, referred to as thermally contracted deformed portion) that is discharged from the first printing apparatus and is greatly thermally contracted and deformed is reversed by the reversing device and is fed to the second printing apparatus. When the thermally contracted deformed portion passes through the upper side of the preheater of the second printing apparatus, adhesion of the web W with the preheater is lowered due to the deformation, the heat cannot be sufficiently obtained from the preheater, and the preheating of the web W before the web enters the heating roll and the pressurizing roll may be insufficient. As a result, the amount of heat that is received by the toner image is insufficient and a local fixing defect occurs.
In order to solve the above problems, for example, in a technology that is disclosed in Japanese Patent Application Laid-open No. 2009-53288, each of the first printing apparatus and the second printing apparatus has a preheater to fix an image to the web W and a mechanism (hereinafter, referred to as “suction mechanism”) to suck the web to the preheater. In this conventional system, the suction mechanism has a mechanism that can change the suction force, and at least the second printing apparatus has a unit that grasps the length of one page of the web W to be printed and a unit that grasps the number of pages of the web W existing between the first printing apparatus and the second printing apparatus. During a period where the web stopped on the preheater of the first printing apparatus passes through the second printing apparatus, the suction force of the suction mechanism is controlled to be increased.
However, in the configuration of this system, when a long web is used, if the suction force in the suction mechanism is increased, this affects the anterior and posterior conveyance forces of the suction mechanism on a conveyance path. As a result, a paper travel is disturbed and a behavior of the web is disturbed in a place where an image is transferred to the web. For this reason, a printed product where an image is blurred and an image quality is bad may be generated.
In the case where the printing apparatus includes a mechanism that contacts the web, such as a pair of rollers nipping the web, when the printing operation is stopped for a long time, the thermally contracted deformed portion is generated, and the same part of the web contacts the corresponding mechanism for a long time, which may result in generating deformation, such as bending, in the portion of the web that contacts the mechanism.
In this state, if the printing restarts, when the web W having the deformed portion passes through the upper side of the preheater, because of the same reason as the reason described above, the preheating of the web may be insufficient, the amount of heat that is received by the toner image may be insufficient, and the local fixing defect may be generated.